This invention relates to the field safety related control systems (SCRS) which are designed to protect the safety of personnel who enter, work in, and leave areas called “cells” where there is automated machinery. In the U.S., these SCRS's are regulated by OSHA.
A few different systems have been devised to allow individuals to enter an automatically functioning cell. Each one of these systems requires stopping automation completely when a worker enters and is within the protected area. For example with the “ Lock Out-Tag Out” system, the automated functioning of the equipment is completely stopped before any person can enter the automated work area, or “cell.” Once the individual enters the automated work area, this method does not have any means to track location of the person in the cell and therefore can not allow automation to resume at any time the system is working in automated mode without risk of the individual getting exposed to the hazard. Another system is known as “Confined Space Entry,” a protocol which requires doing all of the steps in “Lock-Out Tag-Out” but with more rigorous documentation requirements and limiting access only to personnel trained to do a particular job. As far as the tracking of an individual is concerned, the “Confined Space Entry” system has the same level of limitations as the “Lock Out-Tag Out” system. Both these methods rely heavily on administrative measures to eliminate hazards prior to entry into the automated cell by a person.
Another major class of such SCRS systems are known as “Trapped Key” systems. Trapped key systems use fixed barrier guards to form a “gated area” around automated work cells and an interlocked key system at the entry gates. At each entry gate there are two sets of keys, a primary key and one or more secondary key(s). An individual who desires to enter a trapped key controlled cell containing automation is required to remove the primary key from its home receptacle which causes the automation machinery to shut down to permit the individual to enter the gated area as the lock from which the primary key was withdrawn is interlocked with the automation control system. The individual has to insert the primary key into a secondary receptacle and “trap” it in by turning it, which causes one or more secondary keys to be released and the access gate to open. Each individual entering into the work cell is required to carry one secondary key. While one or more secondary keys are missing from the secondary key receptacle(s), the primary key can not be removed and the gate can not be locked, thus preventing resumption of automation in error. In other words, all the secondary keys must be returned to their receptacles to release the trapped primary key so that the primary key can be returned, the gate closed, and the automation restarted.
An example of a trapped key system was disclosed by Bailey, U.S. Pat. No. 6,837,084, assigned to Fortress Interlocks Limited, which described an interlock unit for use with at least one other like unit to form an interlock mechanism which has a top face and opposed pairs of side walls with at least one runner bar mounted in the unit for lateral sliding movement.
Prior trapped key SCRS systems always disable automation any time a person needs to enter into the automated work cell and do not track the location of the individual in the cell. They only function to turn off automation until the primary key is replaced.
SCRS systems which do not utilized trapped keys are also known. For example, Thomson U.S. Pat. No. 5,880,954 disclosed a SRCS designed to safeguard personnel operating hazardous production equipment. The SRCS monitors the machine, the operator, and itself for safe operation and utilizes a non-material barrier such as a light curtain-presence sensing system to sense the intrusion of a person's body into a hazardous area of a machine. The SRCS uses machine feedback and/or operator interface to determine whether a hazardous condition is present. If such condition is present, the hazard is rendered harmless by the time the intruding body member can reach the potential danger area. The system includes separable means for stopping motion of the moving parts of the equipment, starting movement of the movable parts, and detecting faults in sections of the system.
In environments were there is a need to frequently enter the automated cell, there is a significant adverse affect on output or efficiency of the process within the cell due to the disabling or suspending of automation each time a trapped key is removed from its receptacle.
Heckel, U.S. Pat. No. 6,532,508, disclosed a control system for controlling safety-critical processes having a first control unit for controlling a safety-critical process and at least one signal unit linked to the safety-critical process via I/O channels. Among the processes are monitoring of guards, protective doors, light barriers, two-hand switches, and reaction to emergency shut down devices. It describes a field bus connecting said first control unit and said signal unit, and a bus master for controlling communication on said field bus. Said first control unit and said signal unit each comprise safety-directed arrangements for ensuring failsafe communication among each other. Said bus master is connected to said field bus separately from said first control unit and said signal unit.
Barnett, U.S. Pat. No. 6,928,855, disclosed zero speed indicators, i.e., motion detectors, that are used to control the opening of barriers guarding moving machine components. The indicators may be tested by removing them from the components during operation without shutting down production or in certain situations the indicators may be tested during the run down phase of the components caused by machine stop initiations. The tests allow to anticipate and hence prevent hazardous opening of barriers due to a faulty zero speed indication.
Schuster, U.S. Pat. No. 7,076,311, Rockwell Automation Technologies, disclosed a configurable control system for operating an industrial system in a reliable, safety-enhanced manner, which includes storing onto a controller a master program capable of being used to operate a generalized industrial system having a maximum number of safety subsystems of a given type, among which are trapped key subsystems.
Holterman, U.S. Pat. No. 7,116,069, disclosed a safety system intended to ensure the safety of humans working in the area of potentially dangerous machinery in an industrial process which accepts inputs from emergency stop buttons, rope pull switches, safety mats, key switches, light curtains and the like, and stop the operation of equipment based on a command or the presence of a human in a dangerous area. The invention is directed to electric motors, and safety systems may disable those motors to stop the equipment, rather than trapped key systems per se.
Stubbs, U.S. Pat. No. 7,161,261, also assigned to Fortress Interlocks Limited, disclosed a control method and apparatus for a door-locking mechanism which includes an electrically-released latch, to lock the door closed.
Eden, U.S. Pat. No. 7,181,941, disclosed a pin tumbler-type cylinder lock having an auxiliary tumbler stack, the bottom pin of the auxiliary tumbler stack has a recessed underside for receiving a projection on the key to form a detent. When the projection on the key is seated, it prevents the key from being withdrawn from the keyway while the plug is in any rotational position in which the drive and bottom pins are not substantially aligned. Thus, the key is retained whenever the plug has been rotated.
Nakamura, U.S. Pat. Publ. 2004/0215354 disclosed a safety network system constructed by connecting a safety programmable controller (“PLC”) to a safety slave through a safety network which obtains safety input information from a plurality of safety devices connected thereto and transmits information based on the plurality of safety input information in response to a request from the safety PLC. Among the sensors, light curtains which detect incoming persons or parts of a body and shut down system operation are disclosed. Nothing about trapped key systems is disclosed.
Bechtel, U.S. Pat. Publ. 20060212144, disclosed a light barrier contact-less safety device, i.e., a safety device operating without contact has an interface for the transmission of output signals to connectable appliances for signal processing. The output signals from the individual sensors of the safety device operating without contact can be transmitted separately via the interface.
Etherton, U.S. Pat. Publ. 2007/0101873, disclosed a jam detection and safety device for jamming machinery which mentions at paragraphs 0041, 0042, and 0049 trapped key switches such as Fortress brand (68 and 72 in FIG. 3), with a description of use of such switches to protect against inadvertent starting of, for example, balers, when the operator is clearing a jam. See paragraphs 0041-0042. This published application does not disclose the idea of sub-cells controlled by tertiary keys.
Prior art systems require stopping automation completely and do not have any means for tracking the location of the worker in the cell and therefore can not allow automation to resume while a worker is within the cell. Currently there is no safe way to track an individual entering into an automatically functioning work cell to observe the operation or conduct certain type of work from inside the cell while the cell is working under full automation without bypassing the safety mechanism installed on the cell or exposing individuals to the hazards.